This invention pertains generally to the field of integrated optical components for use in fiber optic communication systems, and more particularly it relates to photonic switching. Specifically, the invention is directed to new designs for integrated optical switches which enable such switches to have very high extinction ratios without stressing current and foreseeable fabrication technologies.
For the past few years, optical switching and multiplexing techniques have been seriously considered for future broadband networks. Integrated optical switches will probably play a key role in such applications because of their very large data bandwidth, high-speed capability and integratability. For other applications such as optical instrumentation, optical computing and signal processing, integrated optical switches are also potentially very useful.
Many devices have been proposed or demonstrated for use as integrated optical switches. Examples are directional couplers, reverse delta-beta couplers, X-switches and mode-sorting switches. The major problem encountered by these conventional devices is that their insertion loss and crosstalk are not trivial, and both tend to accumulate within the system in which they are used. The performance of optical systems using these conventional switches is often limited or degraded by these two factors. Recent advancements in optical amplifier technology have demonstrated that optical amplifier gain can compensate for optical loss. If the use of optical amplifiers in a system proves practical, the remaining important issue is crosstalk.
Crosstalk in a system results from the limited extinction ratio that individual switches can achieve. Typical integrated optical switches can achieve an extinction ratio in the range of 20 to 30 dB, if electrical tuning is performed. Although in some cases proper system architectures can be adopted to reduce the accumulation of crosstalk, a more fundamental solution is to increase the extinction ratios of the optical switches. More advanced or critical fabrication technology is often suggested to improve the extinction ratios of the switches. However, only limited improvements have been achieved in this respect. The fabrication in quantity of integrated optical devices with extinction ratios beyond 25 dB becomes very difficult.
In an earlier filed, copending U.S. patent application, Ser. No. 07/289,658, filed Dec. 23, 1988, entitled ULTRA-HIGH-EXTINCTION CASCADED COUPLED-WAVEGUIDE OPTICAL MODULATORS AND OPTICAL GATE ARRAYS, which is incorporated herein by reference as background information, I have disclosed a novel design for 1.times.1 integrated optical modulators which can achieve ultra-high extinction ratios without stressing the fabrication technology. In another earlier filed copending U.S. patent application, Ser. No. 07/414,984, filed Sep. 29, 1989, entitled HIGH-EXTINCTION 1.times.2 INTEGRATED OPTICAL SWITCH, S.-F. SU, inventor, which is also incorporated herein by reference as background information, discloses an integrated optical switch design with a 50 dB extinction ratio. Both of said applications are assigned to the assignee of this application.